Bredolab, which disgorged more than 3 billion malicious emails a day at its peak, spread by planting malicious scripts on legitimate websites. These scripts used browsers exploits and the like to drop the zombie software onto the Windows PCs.

Components of the Bredolab malware were designed to steal usernames and passwords to FTP accounts, creating a means to plant malicious code onto more legitimate sites in the process, further multiplying the spread of infection.

Prospective marks were tricked into visiting compromised sites using spam emails with dodgy HTML attachments that posed as messages from the likes of Facebook, Skype and Amazon. Screenshots of infected email, along with commentary on the botnet and Avanesov's prosecution, can be found in a blog post by Sophos here.

"It's easy to see how such a large network of infected PCs was created, as people clicked on seemingly legitimate attachments and websites, oblivious to the infection that would go on to take control of their PC, and in some cases steal passwords and usernames," commented Graham Cluley, a senior technology consultant at Sophos. "To prevent botnets such as this forming, it is critical that website administrators don't let FTP software remember passwords, and that users are more cautious in the attachments they download."

Avanesov's downfall followed swiftly on the heels of the botnet takedown operation in October 2010.

Dutch police seized control of command & control servers associated with the Bredolab botnet, using this access to display warning messages to users with compromised PCs. Days afterwards, Avanesov was arrested at Yerevan's Zvartnots Airport in Armenia, shortly after he stepped off a late night flight from Moscow.

The 27-year-old is the first person in Armenia to be jailed for violation of Armenia's computer crime laws. Local (English language) reports on Avanesov's sentencing on Tuesday can be found here. ®